Modern digital networks are designed to operate in a multimedia environment for transporting different types of data including pure data, such as files of alphanumeric characters, as well as voice, image, video signals, etc . . . The operation of the network should, naturally ensure compliance with a number of requirements specific to each kind of these signals.
For instance, information can be divided into different types. One type is non-real-time information, i.e. information that can be delivered to an end-user with minor time constraint restrictions. Another type is real-time information that must be delivered to the end-user with a predefined limited-delay restriction. If real-time information is not delivered to the end-user within the predefined time delay period, the information should simply be discarded.
On the other hand, applications using non-real-time information may recover from fairly large and variable time delays resulting from transport from source to destination. However, any loss of non-real-time data may become dramatic, even though techniques have been developed to deal with loss of data.
Different techniques have been developed for transporting data, such as packet switching techniques, wherein digitized data is arranged into so-called bit packets, and circuit switching techniques. The packets may either be of fixed length, e.g., Asynchronous Transfer Mode (ATM) packets, or variable length (VL) nature.
A basic advantage of packet switching over circuit switching is that packet switching permits statistical multiplexing of the different types of data over a link, which optimizes utilization of the transmission bandwidth. A drawback of packet switching compared to circuit switching is that packet switching may introduce jitter and delay in the transported information at the destination. As already noted, jitter or delay may be detrimental for transmission of isosynchronous data, like video or voice.
A basic data transmission network includes switching nodes interconnected by transmission links or trunks, for transporting data from end-users in a dynamic and optimal manner.
A packet switching network may be very complex in architecture and operation. The optimization of such a network requires that each network node be designed to be able to interconnect all kinds of trunks or links without distinction, while also being capable of discriminating between network control data and end user data so the two types of data may be processed appropriately.